Molecular structure of 1,8-dimethylfluoren-9-one.

The molecular and crystal structure of the synthetic 1,8-dimethyl derivative of 9H-fluoren-9-one (F-9-one) has been determined by direct methods from X-ray diffractometric data and refined to an R index of 0.035 over 1216 independent reflections. With a mutual inclination between benzene rings of 178.6 degrees, the molecule is closely planar; of the non-hydrogen atoms, only the oxygen is as much as 0.08 A out of the plane defined by the ring-joining carbons C(10), C(11), C(12) and C(13). Neither the carbonyl bond nor the beach bond C(11)-C(12) differs significantly from the corresponding bonds in F-9-one and the 2,7-diamino compound; C-C bonds involving methyl carbons and the keto carbon are all very close to 1.50 A long (e.s.d. 0.003 A). The C-C(methyl) bonds are bent so that angles C(10)-C(1)-C(14) and C(13)-C(8)-C(15) are about 123 degrees, while the methyl groups are orientated with one hydrogen from each pointing away from the carbonyl group.